Drilling head

ABSTRACT

A drilling head, with a cross-sectional dimension (E) in a direction normal to the drilling axis (A), includes two diametrically opposite, free-standing, prong-shaped support members ( 2 ) provided at a head-side of the drilling head, and a diametrically extending hard material element ( 3 ) connected with the two support members ( 2 ) and which forms at least one cutter ( 4 ) at its head, in an axial direction, side and which lies freely in a central region (Z) of the drilling axis (A) at a stem, in the axial direction, side of the drilling head ( 1 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a forked drilling head for rock materials and, in particular, for an injection self-drilling anchor.

2. Description of the Prior Art

Forked drilling heads (also known as two-prong drilling heads or fish-tail drilling heads) are characterized by a high drilling capacity in a comparative soft rock material, e.g., when drilling the cap rock when mining the coal semi-coke.

Such mass-produced drilling heads, to which the present invention is limited, have, at a drilling diameter between 25 mm and 60 mm, a small degree of complexity. So the number of separate parts, such as hard material inserts that form cutters, is limited, for manufacturing reasons, to a small number, maximum to five parts. When the drilling head is used as a one-time usable injection self-drilling anchor, with an anchor-serving tubular stem of the drilling head being glued to a bore wall with a twin-component resin mortar, the retaining of the dimensional accuracy of the bore cross-sectional dimension becomes of a very high importance. This is because it is the cross-sectional dimension that determines the strength of the annular channel that is filled with the twin-component resin mortar.

According to International Publication WO 8901086 and German Publication DE 41 34 425, a forked rock drilling head, which is equipped with hard material, has at its head side, two diametrically opposite, radially and circumferentially freely extending, prong-shaped support members, with a hard metal cutting element brazed to each of the support members. At the base between the support members, there is located an opening of a rinsing bore extending coaxially with the drilling axis. However, with two separate hard metal cutting elements, it is difficult to realize a bore with a cross-sectional dimension within narrow tolerance limits because the cutting elements can be displaced relative to each other during brazing. In addition, during brazing, the hard metal cutting elements are secured to the respective support members separately.

German Publication DE 34 36 128 discloses a pot-shaped drilling head for drilling bores for injection self-drilling anchors and equipped with a single, diametrically extending, hard metal plate. The hard metal plate, which has two diametrically opposite cutting edges, is supported by the drilling head along its entire axial length. The drawback of this drilling head, in comparison with the forked drilling heads, consists in its small drilling capacity during drilling of bores in gallery roofs of coal mines.

Accordingly, an object of the present invention is to provide a forked drilling head suitable for mass production.

Another object of the present invention is to provide a forked drilling head capable to maintain a high dimensional accuracy of a bore cross-width.

SUMMARY OF THE INVENTION

These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a drilling head having at its head side, two diametrically opposite, free-standing, prong-shaped support members, a diametrically extending hard material element connected with the two support members and which forms at least one cutter at its head, in an axial direction, side and which lies freely in a central region of the drilling axis at its stem, in the axial direction side. The diametrically extending hard material element itself defines the dimensional accuracy of the bore cross-sectional dimension, so that the dimensional accuracy does not depend on exact fixing of the hard material element on the support members during the assembly of the drilling head.

Advantageously, there is formed at a bottom, which is formed between the two support members, at the head, in the axial direction, side of the drilling head, an opening of a rinsing bore coaxial with the drilling axis. Thereby, the central part of the hard material element, which lies freely in the central region of the drilling axis and which becomes very hot during the drilling process, is directly cooled by the rinsing water. As a result, a smaller portion of heat should be removed from the area that connects the hard material element with the support members and which has a heat transition coefficient. This increases the usable life of the drilling head.

Advantageously, a diametrical free space between the two support members amounts to at least a fifth of the cross-sectional dimension of the drilling head. Thereby, a high drilling capacity is reached when drilling the relative soft rock material such as cap rock that prevails in mines with coal semi-coke. In addition, the opening cross-section is sufficiently large for wet drilling with a low water pressure from 5 to 30 bar.

Advantageously, the hard material element is connected with the support members in material-locking manner (i.e., being integral with each other), e.g., is brazed, which provides for a connection capable to withstand high loads.

Advantageously, the hard material element is formed as a thin hard material plate with a thickness of less than a tenth of the cross-sectional dimension of the bit.

Thereby, the bending stiffness of the hard material element, which is proportional to a cube of thickness, is sufficiently low to prevent any damage of the connection from bending vibrations of the support members caused by drilling.

Advantageously, the hard material element has a thickness reduction in the radial region of the drilling axis, e.g., arcuate notches provided on opposite sides. Thereby, this hinge region has a particular low bending stiffness.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

FIG. 1 a longitudinal cross-sectional view of a drilling head according to the present invention along line I-I in FIG. 2; and

FIG. 2 a plan view of the drilling head shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A forked drilling head 1 according to the present invention, which is shown in FIGS. 1-2, has a drilling axis A, a cross-sectional dimension E in a direction normal to the drilling axis A, of 60 mm, and two diametrically opposite, with respect to the drilling axis A, radially and circumferentially free-standing prong-shaped support members 2. Both supports are brazed, respectively, with a single, diametrically extending hard material element 3 which forms, at its head, in the axial direction, side two cutters 4. The hard material element 3 lies freely at its stem side, in the central region Z of the drilling axis A. At the head in the axial direction-side, bottom of the drilling head 1, which is formed between the two support members 2, there is provided an opening 5 of a rinsing bore 6 coaxial with the drilling axis A. A diametrically extending free space F between the two support members 2 of 20 mm amounts to a third of the cross-sectional dimension. The hard material element 3 is formed as a thin hard material plate having a thickness D of 3 mm, i.e., one twentieth of the cross-sectional dimension E, and having an arcuate notch 7 on each of its sides in the radial region R of the drilling axis A.

Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims. 

1. A drilling head having a drilling axis (A) and a cross-sectional dimension (E) in a direction normal to the drilling axis (A), the drilling head comprising, at a head side thereof, two diametrically opposite, free-standing, prong-shaped support members (2); and a diametrically extending hard material element (3) connected with the two support members (2), forming at least one cutter (4) at a head, in an axial direction, side thereof, and lying freely in a central region (Z) of the drilling axis (A) at a stem, in the axial direction, side thereof.
 2. A drilling head according to claim 1, comprising at a bottom formed between the two support members (2) at the head, in the axial direction, side of the drilling head, an opening (5) of a rinsing bore (6) coaxial with the drilling axis (A).
 3. A drilling head according to claim 1, wherein a diametrical free space (F) between the two support members (2) amounts to at least a fifth of the cross-sectional dimension (E).
 4. A drilling head according to claim 1, wherein the hard material element (3) is connected with the support members (2) in a material-locking manner.
 5. A drilling head according to claim 1, wherein the hard material element (3) is formed as a thin hard material plate having a thickness (D) less than a tenth of the cross-sectional dimension (E).
 6. A drilling head according to claim 1, wherein the hard material element (3) has a reduction of thickness (D) in a radial region (R) of the drilling axis (A). 